1. Field of the Invention
The present invention relates to an energy storing device capable of storing energy and discharging the stored energy by utilizing an elastic deformation of an elastic body. More particularly the present invention relates to an energy storing device wherein elastic strain energy is stored in a stretched elastic cord wound on a drum.
2. Description of the Prior Art
Energy storing devices which can store energy by utilizing an elastic deformation of an elastic cord are disclosed in Japanese utility model publications Nos. SHO 61-38360, SHO 61-38361, SHO 61-38362, SHO 61-38363, SHO 61-38364 and SHO 61-38365, and Japanese patent publication No. SHO 61-41649 etc.
The approximate arrangement and function of the conventional energy storing devices disclosed in the above publications are explained with reference to FIGS. 23 and 24. An energy storing device 1 has a drum 2. An elastic cord 3 spirally wound on the drum 2 has one end fixed on the drum 2 and the other end fixed on a frame 4. A torque transmission device 5 driven by an engine 6 of an automobile is connected to drum 2 via a clutch 7. During engine deceleration, clutch 7 engages, the rotation of torque transmission device 5 rotates drum 2, thereby winding elastic cord 3 on the drum 2. Because the other end of the cord is fixed to frame 4, the cord stretches, and elastic strain energy is stored in the stretched elastic cord 3 wound on the drum 2. When a sufficient amount of elastic strain energy is stored, clutch 7 disengages, stopping the rotation of drum 2. When engine 6 is started or accelerates, clutch again engages, drum 2 is reversely rotated by the wound elastic cord 3, and elastic strain energy stored in the elastic cord 3 is discharged. The discharged energy is utilized to assist accelerating or starting of th automobile.
In the above energy storing device 1, elastic cord 3 is wound on drum 2 via carrier 8, as shown in FIG. 24. The carrier 8 permits wound elastic cord 3 to move freely along the periphery of the drum 2 in the circumferential direction. Therefore, when elastic cord 3 is stretched and wound on the drum 2, the strain of the elastic cord 3 occurs over the entire length of the elastic cord 3.
However, when the peripheral displacement due to the rotation of drum 2 becomes large, the tension of elastic cord 3 also becomes large and places a large load on the drum. Accordingly, the energy storing device 1 must be strong and rigid to endure the large load, causing the device to be large and heavy. Such a structure increases the cost of the device, and adds to the weight of a vehicle, thereby reducing fuel economy when the device is applied to the vehicle.
In another type of elastic energy storing device, the entire length of the elastic cord is not strained uniformly but a part of the elastic cord is strained to a great and constant extent, the strained portions of the elastic cord are wound on a drum continuously, the proportion of the strained and wound portions of the elastic cord is gradually increased, and the elastic strain energy is stored in the strained elastic cord wound on the drum. Such a device is disclosed in, for example, Japanese patent publication No. SHO 49-96144. Such a device can be prevented from having a large-sized and heavyweight structure. The device disclosed in Japanese patent publication SHO No. 49-96144 is shown in FIG. 25. The device has two drums 9 and 10, an elastic cord 11 is wound between drums 9 and 10, and drums 9 and 10 are rotated in the same direction via pulleys 12 and 13 and belt 14. A similar device shown in FIG. 26 has substantially the same function as the device disclosed in Japanese patent publication No. SHO 49-96144. In FIG. 26, two parallel drums 15 and 16 having different diameters have an elastic cord 17 extended obliquely between them and are mechanically connected by gears 18 and 19 so as to rotate in opposite directions.
In devices having two drums, as shown in FIGS. 25 and 26, if the initial strain of the elastic cord wound onto the smaller diameter drum (drum 9 or 15) is zero, the discharged energy becomes zero and output efficiency of the device becomes zero. (The reason is described later.) Therefore, if a cord having poor elasticity is used, there occurs a problem that the output energy becomes almost zero because not enough initial elastic strain can be taken.